The overall objective of this project is to investigate the actions of the photoreceptor neurotransmitter candidates L-glutamate (L-Glu) and L-aspartate (L-Asp) in the distal retina of goldfish. Neurotransmitters released from photoreceptors will be analyzed directly by high pressure liquid chromatography with o-phthalaldehyde fluorescence detection. Further, the electrophysiological response to Glu and Asp and their analogs will be studied on enzymatically dissociated and cultured isolated horizontal and bipolar cells using patch clamp and whole cell voltage clamp techniques. These electrophysiological experiments should provide a comprehensive picture of the pharmacological and electrophysiological charateristics of membrane receptors and ionic channels for Glu, Asp and their analogs on these cells. Results obtained on isolated cells will also be corroborated by analogous experiments on the intact excised retina. In addition, the uptake of radiolabelled Glu and Asp into photoreceptors and Mueller glial cells will be investigated by autoradiographic and biochemical techniques. The aim in these experiments is to determine to what extent these two transport systems are involved in inactivating photoreceptor transmitters after release and how this inactivation is regulated physiologically. The proposed research is expected to contribute to our understanding of the molecular mechanisms underlying the first stages of visual information processing in the retina. It is also expected to provide basic knowledge which may increase our understanding of the pathogenesis of neurological disorders (e.g. Huntington's chorea, epilepsy) which may involve aberrant function of Glu/Aspergic neural circuitry.